1. Field of the Invention
This invention relates to an ion source of the penning ionization gauge (PIG) type that can be used for ion-beam deposition, ion implantation, heavy ion technology, and the like.
2. Description of the Prior Art
As a conventional PIG-type ion source, there is the self-heating type ion source shown in FIG. 5, which was developed by Bennett (Junzo Ishikawa, Ion Source Technology, Ionics, 1986, p. 462). In this ion source, a gas such as argon is supplied into the cylindrical anode 1 via the gas inlet 3. When a magnetic field in the X-direction arising from solenoids 4 and an electric field formed by a power supply 5 in the space between the anode 1 and the cathodes 2 are set at appropriate levels, electrons emitted from the cathodes 2 move by the combination of their cyclotron movement along the magnetic lines of force, their drift movement taking place by means of the orthogonal electromagnetic field, and their oscillatory movement taking place between the two cathodes 2. Then, the electrons collide with neutral particles, so that plasma is produced until the energy of the electrons is almost exhausted. In this way, plasma is produced by a discharge (i.e., an emission of electrons from the cathodes 2) in the above-mentioned PIG-type ion source, and, by an ion-extraction electrode 8 connected to a power supply 7, the ions of the plasma are extracted in a beam form in the Y-direction from the slit-shaped ion exit 6 in the side surface of the anode 1.
In this way, the conventional ion source mentioned above is constructed so that a magnetic field that causes the PIG discharge is applied in the axial direction and ions are extracted through a slit; for this reason, the ion beam extracted through the slit is shaped like a rectangle, which makes it difficult to achieve uniform radiation over a large surface area of samples such as silicon wafers or the like to be treated with ion beams.